Autoimmune pancreatitis (AIP) is a chronic inflammatory condition believed to be caused by the immune system attacking the pancreas. It responds well to steroid treatment. Two subtypes of AIP are recognized: Type 1 and Type 2.
Type 1 AIP, also known as IgG4-related pancreatitis, is part of a broader condition called IgG4-related disease (IgG4-RD), which often affects multiple organs, including the pancreas, bile ducts, liver, salivary glands, kidneys, and lymph nodes.
Type 2 AIP, also known as idiopathic duct-centric pancreatitis, appears to primarily affect only the pancreas, although about one-third of individuals with Type 2 AIP may also have inflammatory bowel disease.
AIP is a rare condition that has been recently recognized and can be misdiagnosed as pancreatic cancer. The two conditions share similar signs and symptoms but require very different treatments, making accurate differentiation crucial.
Symptoms
Autoimmune pancreatitis can be difficult to diagnose, often presenting with no symptoms at all. When symptoms do occur, they may resemble those of pancreatic cancer, including:
- Dark urine
- Floating stools
- Jaundice (yellowing of the skin and eyes)
- Upper abdominal pain or mid-back pain
- Nausea and vomiting
- Weakness or excessive fatigue
- Loss of appetite or a feeling of fullness
- Unexplained weight loss
The most common sign of autoimmune pancreatitis, observed in about 80% of patients, is painless jaundice, caused by obstructed bile ducts. AIP can also lead to weight loss. Many individuals with AIP have masses in the pancreas and other organs, which can be misdiagnosed as cancer.
- Affected Organs:
Type 1 AIP: Can affect multiple organs beyond the pancreas.
Type 2 AIP: Primarily affects only the pancreas, though it may be associated with other autoimmune conditions like inflammatory bowel disease. - Response to Treatment:
Type 1 AIP: Responds quickly to steroid treatment.
Type 1 AIP: Is likely to relapse if treatment is discontinued.
Causes
The exact cause of autoimmune pancreatitis remains unknown. Like other autoimmune diseases, it involves the immune system attacking healthy body tissue.
Risk Factors
The two types of AIP have different prevalence rates in various parts of the world. In the United States, approximately 80% of individuals with autoimmune pancreatitis have Type 1.
- Individuals with Type 1 AIP:
- Typically over the age of 60.
- More commonly male.
- Individuals with Type 2 AIP:
- Often over the age of 40 (one or two decades younger than those with Type 1).
- Can be both male and female.
- More likely to have inflammatory bowel disease, such as ulcerative colitis.
Complications
Autoimmune pancreatitis can lead to various complications:
- Pancreatic Insufficiency: AIP may impair the pancreas’s ability to produce sufficient enzymes, resulting in symptoms like diarrhea, weight loss, metabolic bone disease, and vitamin or mineral deficiencies.
- Diabetes: Damage to the pancreas, which produces insulin, may lead to diabetes, requiring oral medications or insulin therapy.
- Pancreatic Calcifications or Stones.
While treatments for autoimmune pancreatitis, such as long-term steroid use, can cause complications, individuals receiving treatment generally have a normal life expectancy.
There is no established link between AIP and pancreatic cancer.
Diagnosis
Autoimmune pancreatitis (AIP) is difficult to diagnose because its signs and symptoms closely resemble those of pancreatic cancer. However, an accurate diagnosis is extremely important, as undiagnosed cancer can lead to delays or failure to receive necessary surgical intervention.
Individuals with AIP often exhibit general enlargement of the pancreas but may also have a mass in the pancreas. To establish the diagnosis and determine the type of AIP, blood tests and imaging studies are essential.
Testing
No simple test can identify autoimmune pancreatitis. Until recently, varying diagnostic approaches worldwide have complicated the diagnosis. Sometimes, surgery is necessary to rule out pancreatic cancer.
Special tests may include:
- Imaging Tests: Evaluations of the pancreas and other organs may include CT scans, MRIs, endoscopic ultrasounds (EUS), and endoscopic retrograde cholangiopancreatography (ERCP).
- Blood Tests: Elevated levels of an immunoglobulin called IgG4, produced by the immune system, will be sought. Individuals with type 1 AIP, but not type 2, will have high levels of IgG4 in the blood.
However, a positive test does not necessarily mean that you have the disease. A small number of individuals without autoimmune pancreatitis, including some with pancreatic cancer, also have elevated IgG4 levels in their blood.
- Endoscopic Biopsy: In this test, pathologists analyze a sample of pancreatic tissue in the laboratory. AIP has a distinct appearance that is easily recognized under a microscope. Doctors insert a small tube (endoscope) through the mouth into the stomach and, guided by ultrasound, obtain tissue from the pancreas using a special needle.
The challenge is to obtain a tissue sample large enough for analysis rather than just a few cells. This procedure is not widely available, and results may not be definitive.
- Steroid Test: Since autoimmune pancreatitis is the only pancreatic disorder known to respond to steroids, doctors sometimes use a trial course of this medication to confirm the diagnosis. The response to corticosteroids is measured using CT scans and improvements in serum IgG4 levels.
Treatment
Biliary Stenting: Before starting medication, doctors sometimes place a tube to open the bile ducts (biliary stenosis) in individuals with obstructive jaundice symptoms. However, jaundice often improves with steroid treatment alone. This procedure may be recommended if the diagnosis is uncertain.
Steroids: Symptoms of autoimmune pancreatitis often improve after a short course of prednisone or prednisolone. Many people respond quickly, sometimes dramatically. Occasionally, individuals may improve without any treatment.
Immunosuppressants and Immunomodulators: About 30 to 50 percent of the time, AIP may relapse, requiring additional treatment, sometimes long-term. To reduce severe side effects associated with prolonged steroid use, doctors often add medications that suppress or modify the immune system. You may be able to stop taking steroids altogether.
Immunosuppressants and immunomodulators include mercaptopurine, azathioprine, etc. Generally, they have been used in small sample groups and their long-term benefits are still being studied.
Treatment for Pancreatic Insufficiency: If you have insufficient enzymes in your pancreas, you may need supplemental enzymes. If supplements are necessary, your doctor will prescribe pancreatic enzymes.
Diabetes Treatment: If you have diabetes, appropriate treatment will be required.
Monitoring for Involvement of Other Organs: Type 1 AIP is often associated with involvement of other organs, including swollen lymph nodes and salivary glands, biliary involvement, liver inflammation, and nephropathy. While these signs may diminish or completely resolve with steroid treatment, your doctor will continue to monitor your condition.